High temperature plastic-ceramic castable

ABSTRACT

A HIGH TEMPERATURE, HIGH TENSILE STRENGTH PLASTIC-CERAMIC CASTABLE SUITABLE FOR USE IN EASILY CASTING INTO MOLDED SHAPES PRIOR TO CURING; THE CURE CASTABLE HAVING QUALITIES OF BEING WEAR RESISTANT, CHAFE RESISTANT, CORROSION RESISTANT HEAT RESISTANT, AND SUBSTANTIALLY NONSHRINKABLE. THE CASTABLE CONSISTS OF A MONOLITHIC COMPOSITION PRODUCED BY ADMIXING A REFRACTORY OXIDE FILLER, AN EPOXY RESIN AND AN ALIPHATIC, AROMATIC OR MIXTURE THEREOF POLYFUNTIONAL AMINE CURING AGENT.

June 1, 1971 Filed May 15. 1968 SHRINKAGE IN. /IN. /FXlO-6 J. a. BAILEY, .13., ETAL 3,582,517

HIGH TEMPERA'IURE PLASTIC-CERAMIC CASTABLE 6 Sheets-Sheet 1 .l4 l2 FIG- la .IO I .0 I .06

-8 e-n l4-28 28-48 GRAIN SIZE CURE SHRINKAGE a FIG- 1b 8-44 28-48 GRAIN SIZE THERMAL EXPANSION ENTQRS JOHN G. BAILEY, JR.

CLARENCE M. HEAD, JR.

CLARENCE W. PHILLIPS June 1, 1971 J. G. BAILEY, JR., ETAL HIGH TEMPERATURE PLASTIC-CERAMIC .CASTABLE Filed May 13. 1968 6 Sheets-Sheet I LL 0 $3 a In E 3 5 1g? Ha 1 v 5% d w 2 8 8 o c LL c O c O o o o o 8 9 g g, 3 2 .2-

I v l S d HHfildfiH :10 00W 9 m VI 3 m i i2. DLU

":25 o I Q o P 2 O C O O o o 3 3 '3 '8 Q H l S d 3UnldflH d0 COW l (D INVENTORS. .u- JOHN G. BAILEY. JR.

CLARENCE M. HEAD, JR. CLARENCE W. PHILLIPS June 1, 1971 B JR" EI'AL 3,582,517

HIGH TEMPERATURE PLASTIC-CERAMIC CASI'ABLE Filed May 13. 1958 6 Sheets-Sheet 5 6| en 9E1 005: GRAIN T0 RESIN RATIO BY WEIGHT EXPANSION Q-Ol X do/Nl/ NI NOlSNVdX3 WVWHBHL :10 iNBlOlzHHOO .0 cu $2 u 9Il IOII SHRINKAGE CURE OJ 6 I GRAIN TO RESIN RATIO BY WEIGHT 5 |NVENTORS N 39WN|BH$ JOHN G. BAILEY. JR.

CLARENCE M. HEAD, JR. CLARENCE PHILLIPS By gent FIG- 2d FIG- 2c June 1, 1971 M Y, EI'AL 3,582,517

HIGH TEMPERATURE PLASTIC-CERAMIC CASTABLE Filed May 15. 1968 e Sheets-Sheet 4.

4:1 6 1 1:1 8:1 9:1 10:1 GRAIN TO RESIN RATIO BY WEIGHT MOD OF RUPTURE AT 350 F Ell OII

O IO N '1 s11 aumdna .-10 now 8 8 O 0 ID V 2Z1 GRAIN TO RESIN RATIO BY WEIGHT MOD. OF RUPTURE AT ROOM TEMP.

NV NT RS I 'S'd BHfli 50 JOHIII G? BACILEYJR.

June 1, 1971 j BAlLEY, JR" EIAL 3,582,517

HIGH TEMPERATURE PLASTIC-CERAMIC CASTABLE 6 Sheets-Sheet 5 Filed May 13. 1968 AA mm MM UU LL AA A mm L% AF 200 TEMPERATURE ('F) TEMPERATURE EFFECTS ON MODULUS OF RUPTURE OF ALUMINA FILLED EPOXY INVENTORS JOHN G. BAILEY, JR.

CLARENCE M. HEAD, JR. CLARENCE W. PHILLIPS Aerit' June 1, 1971 J. G. BAILEY. JR ETAL 3,582,517

men ramrsauuam rmswxc-cammc CAS'IABLE 6 Sheets-Sheet. 6

INVEN TORS Filed May 13. 1968 m m m m F i mnm m7 m muwmmm m A wmwumm m m m m m m w M7/////////////// /mm%////// h... owns \A. w7/////// .002 mm S 7/ m//// mm T m m mZ//%//////////////////////////////////%///////%/////// m m. m. m. m. m. m m m o I 3' md mmnhmDm m0 002 JOHN G. BAILEY, JR.

CLARENCE M. HEAD, JR.

FIG- 4 CLARENCE W. PHILLIPS United States Patent Office Patented June 1, 1971 3,582,517 HIGH TEMPERATURE PLASTIC-CERAMIC CASTABLE John G. Bailey, Jr., Marietta, and Clarence M. Head,

Jr., Atlanta, Ga., and Clarence W. Phillips, Ormond Beach, Fla., assignors to Lockheed Aircraft Corporation, Burbank, Calif. Continuation-impart of application Ser. No. 423,438,

Jan. 5, 1965. This application May 13, 1968, Ser.

Int. Cl. C08g 51/04 US. Cl. 260-37EP 6 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of application Ser. No. 423,438, filed Jan. 5, 1965, by John G. Bailey, Jr. et al. and assigned to the same assignee this application is assigned to; said prior application now abandoned. I This invention relates to a plastic-ceramic composition and is more particularly concerned with a refractory oxide-epoxy composition, to articles made therefrom and to the process of making the same.

In the past, plastics have been used for binding aggregates together. Such prior art compositions have been used for wallboard, insulation material, artificial stone, and the like.

Indeed, resins impregnated with finely divided iron compounds such as magnetic iron oxide have been used for forming magnetic cores and resin impregnated with Fiberglas has had quite wide acceptance for forming structural parts of boats, automobiles, and the like.

Heretofore, it has been believed that aggregates in admixture with a condensation resin had uses limited to low temperature and relatively low tensile strength applications. Contrary to prior art beliefs and practices we have discovered that an admixture of refractory oxide and epoxy resin, the refractory oxide including as a major constituent thereof aluminum oxide, has unexpectedly high tensile strength and is capable of extended use at elevated temperatures in excess of, for example, 250 F. The fact that the admixture of refractory oxide and epoxy resin can be cast into a variety of prescribed shapes prior to being cured and has relatively low shrinkage when cured to final shape enables the composition to be used in a variety of articles including being shaped into matrices or molds from which duplicate products may be formed.

The monolithic composition of the present invention is produced by admixing aluminum oxide to an epoxy resin which in such admixture is cured to the C-stage in a shape defined by a mold into which the mix in the form of a slurry is poured.

An object of this invention is to provide a plasticceramic having high strength characteristics at both high and low temperatures.

A further object of this invention is to provide a low cost preparation of a plastic-ceramic material, using conventional equipment in such a production.

A further object of this invention is to provide a plasticceramic which is able to be molded in a variety of shapes and forms.

A still further object of this invention is to provide a plastic-ceramic material that has the qualities of being wear resistant, chafe resistant, corrosion resistant, heat resistant, and is substantially nonshrinkable.

Another object of the invention is to provide a process of producing a monolithic body, the process being readily and easily carried out using material which is readily available at reasonable cost.

Another object of the present invention is to provide a monolithic body which is suitable for use as an element of a forming tool.

Other objects of this invention will become more apparent from the description which follows in which:

FIGS. la, 1b, 1c and 1d are graphs showing the effects of varying the grain size of alumina in the composition;

FIGS. 2a, 2b, 2c and 2d are graphs showing the effects of varying the alumina grain to resin ratio in the composition;

FIG. 3 is a graph showing the temperature effects on the modulus of rupture of alumina filled epoxy;

FIG. 4 is a bar graph showing the effects of the addition of oxides other than alumina in the mixture on the modulus of rupture; and

FIG. 5 shows an example of how reinforcing rods are installed in a mold so that a casting able to withstand large bending loads may be formed.

The castable formulations described herein were developed for use in fabricating heated forming tools for plastic-Fiberglas parts. Such tools require high compressive strength at high operating temperature, good abrasion resistance and smooth working faces. Ease of fabrication is a necessity due to cost requirements. Other applications of this product include: heated and room temperature metal forming dies, models, surface plates, lavatories, sinks and fixtures, and low cost corrosion and heat resistant hardware. It should be appreciated that many other applications of this product will undoubtedly be conceived.

Generally speaking, the objects of this invention are achieved by controlling the ratio by weight of resin to filler and/or the ratio by weight of resin to curing agent in the composition.

More specifically, the plastic-ceramic compositions of this invention, which are capable of being molded, are produced by blending a high temperature, high pressure resistant epoxy monomer, a ceramic filler grain and a curing agent and then curing the blended or mixed materials. These epoxy resins are well known in the art and among others they may be diglycerl ethers (for example, epichlorohydrin bisphenol-A and epichlorohydrin acetone), novolac (for example, a resin produced by Dow Chemical CompanyDow D.E.N. 438), and peracetic acid resins (for example, a resin of Union Carbide, ER 201). The filler grains are members selected from the group consisting of alumina and mixtures of alumina with any of a variety of optional additives, such as CaO, MgO, TiO or ZrO -SiO The curing agent is a polyfunctional amine of the general formula in which R is an aliphatic long chain hydrocarbon of from 1 to 8 carbon atoms, R is a member selected from the group consisting of H and a long chain saturated hydrocarbon of from 1 to 8 carbon atoms, and n is 1 or greater, as in the case of a triamine wherein It would be 2. R may also be an aromatic grouping of from 1 to 2 phenyl groups. Thus, R may be either aliphatic or aromatic. Further, the curing agent may be a mixture of both aliphatic and aromatic polyfunctional amines.

Various ceramic filler grain sizes have been experimented with and FIGS. 1a through 1d show the various efiects of different alumina grain sizes. FIG. 1a shows that the cure shrinkage increases as the grain size is increased; FIG. 1b shows that the coefiicient of thermal expansion of the castable decreases as the grain size increases; FIG. lc shows that at room temperature the modulus of rupture increases as the grain size increases; and FIG. 1d shows that at 350 F. the modulus of rupture increases as the grain size increases. A comparison between FIGS. and 1d shows that the modulus of rupture is higher at room temperature than at elevated temperatures.

The grain distribution range is chosen as a logical compromise between numerous opposing variables including cure shrinkage, thermal expansion, modulus of rupture, thermal stability of mechanical properties, modulus of elasticity, material costs, ease of handling, etc. As the graphs indicate this comparison involves a trade-off of one desirable property for another since a larger grain size provides a higher modulus of rupture at room tempeature and at elevated temperatures and a lower coeflicient of thermal expansion; however, cure shrinkage becomes excessive as the grain size increases, which puts a practical limit on grain size. Obviously, the application to which the castable is to be put and the particular qualities most desirable under each particular circumstance will determine the grain size in the mixture.

The ratio by weight of resin to filler may vary from as high as 1 of resin to around 6 of filler to as low as l of resin to around 10 of filler. The exact ratio being determined by the end product properties desires such as minimum cure shrinkage, low coefiicient of thermal expansion, viscosity of the mixture, and the like.

An inspection of FIGS. 2a through 20! shows a range of ratios of ceramic fill to epoxy resin which have been found to provide optimum performance for each condition. FIG. 2a shows that a mixture of below six parts by weight of fill to one part by weight of resin begins to result in excessive cure shrinkage, and FIG. 2b shows that there is a sharp rise in the coefiicient of thermal expansion below the ratio of six to one. Accordingly, if cure shrinkage and thermal expansion are critical factors in the use to which the castable is to be applied the six to one fill to resin ratio might be the lower practical limit with which acceptable results can be obtained. As the fill to resin ratio gets higher the viscosity of the mixture increases and the mixture becomes difficult to handle. It has been found that a ten to one fill to resin ratio is the upper practical limit because of the high viscosity of the mixture. As shown in FIG. 20 the modulus of rupture at room temperature is at its optimum when the castable has been mixed with an eight to one grain to resin ratio. Also, in-

spection of FIGS. 2a and 2b shows that the eight to one ratio is in an acceptable portion of the cure shrinkage curve and the thermal expansion curve. However, under certain circumstances it might be desirable to form the castable with a fill to resin ratio above or below eight to one. For instance, FIG. 2d shows that if the castable is to be used at 350 F., a six to one fill to resin ratio provides the best modulus of rupture. Also, if optimum cure shrinkage and thermal expansion characteristics are of primary concern a ten to one fill to resin ratio would be most desirable. Obviously, as with choosing grain size, the application to which the castable is to be put and the particular qualities most desirable under each particular circumstance will determine the fill to resin ratio.

The following examples illustrate the various properties obtainable with various fill to resin ratios:

EXAMPLE I The ceramic fill comprising alumina grain passed through a mesh sieve was dry mixed to obtain an even size distribution of the grains therein and then slightly heated to about 150 F. for approximately two hours to remove by evaporation any water that might have been present therein. The epoxy resin, epichlorohydrin-bisphe no] A, was heated in an oven at 250 F. for approximately ten minutes until fumes appeared. One part by weight of the hotresin was. then poured into four. parts by weight of the fill and the batch was throughly mixed. During the mixing process a catalyst, diethylene triamine, was added. The mixture was then poured into a mold and vibrated to remove bubbles therefrom. The mixture was vibrated between three and four minutes at 2,400 'to 3,600 vibrations per minute at one-hundredth (0.01) inch minimum amplitude. The curing proceess was begun immediately after the initial set occurred. The A-stage cure was accomplished by heating the casting to F. for two to three hours. After the A-stage cure the casting was removed from the mold and surface bubble holes and chips were repaired. The B and C curing stages were accomplished b heating periods of two hours duration at 250 F. and at 350 F., respectively.

Upon measuring and testing the castable after the casting process was completed, it was found that its cure shrinkage was approximately 0.36 percent of its size; its thermal expansion coefficient was approximately 15 X10- inches per inch per degree fahrenheit; its modulus of rupture at room temperature was approximately 8,000

pounds per square inch; and at 350 F. its modulus of rupture was approximately 4,850 pounds per square inch.

EXAMPLE II A mixture of six parts by weight of fill to one part by weight of resin was prepared in a process similar to that of Example I, the only difference in this example and Example I being the fill to resin ratio. Upon testing this castable after the casting process was completed it was found that its cure shrinkage was approximately 0.28 percent of its size; its thermal expansion coefficient was approximately l2 10* inches per inch per degree Fahrenheit; its modulus of rupture at room temperature was approximately 9,200 pounds per square inch; and at 350 F. its modulus of rupture was approximately 4,900 pounds per square inch.

EXAMPLE III A mixture of seven parts by weight of fill to one part by weight of resin was prepared in a process similar to that of Example I, the only difference being the fill to resin ratio. Upon testing this castable after the casting process was completed it was found that its cure shrinkage was approximately 0.22 percent of its size; its thermal expansion coefficient was approximately 12.5)(10 inches per inch per degree Fahrenheit; its modulus of rupture at room temperature was approximately 9,800 pounds per square inch; and at 350 F. its modulus of rupture was approximately 5,000 pounds per square inch.

EXAMPLE IV A mixture of eight parts by weight of fill to one part by weight of resin was prepared in a process similar to that of Example I, the only difference being the fill to resin ratio. Upon testing this castable after the casting process was completed it was found that its cure shrinkage was approximately 0.18 percent of its size; its thermal expansion coefficient was approximately 103x10- inches per inch per degree Fahrenheit; its modulus of rupture at room temperature was approximately 10,300 pounds per square inch; and its modulus of rupture at 350 F. was approximately 3,500 pounds per square inch.

EXAMPLE V A mixture of nine parts by weight of fill to one part by weight of resin was prepared in a manner similar to that of Example I, the only difference being the fill to resin ratio. Upon testing this castable after the casting process was completed it was found that its cure shrinkage was approximately 0.14 percent of its size; its thermal expansion coeflicient was approximately 8.4 10- inches per inch per degree Fahrenheit; its modulus of rupture at room temperature was approximately 8,700 pounds per square inch; and at 350 F. its modulus of rupture 6 EXAMPLE VIII The exact process of Example VII was repeated except the ratio of curing agent to resin was fifty to one hundred. This product was tested and found to have a module 10"... 1 pbW resin, 8 pbW fill (70% Alm -30% TiO 11 1 pbw resin, 8 pbw fill (70% A11o330% zircon; 12"... 1 pbw resin, 8 pbW fill (50% Alz03-50% zircon 13 1 pbw resin, 8 pbw fill (90% M m-10% MgO) was approximately 4,000 Pounds Per Square inch 5 of rupture at 70 F. and 3,875 p.s.i. and at 350 F. of EXAMPLE VI 2:100 EXAMPLE IX A mixture of ten parts by weight of fill to one part by weight of resin was prepared in a process similar to that The exac? Procedure of Example VII was followed of Example I, the only difference being the fill to resin F the,resm was a novolacflfype g l i y Q ratio. Upon testing this castable after the casting process resin D 43 g y ennui was completed it was found that its cure shrinkage was agent 9 g f i un 5 twenty' ve an approximately 0.14 percent of its size; its thermal expanzi Y g t d r6 31 fto d ways one to sgvtlen, sion coefficient was approximately 8x10 inches per pro g t 232 to g P i inch per degree Fahrenheit; its modulus of rupture at 15 g l ig o a an a room temperature was approximately 6,500 pounds per EXAMPLE X square inch; and at 350 F. its modulus of rupture was 2,800 pounds per square inch. The exact procedure of Example IX was followed ex- The ratio by Weight of resin to curing agent may vary cept the resin was a eracetic acid type as reduced by n I p a u p from as low a ratio of one hundred parts of resin and Union Carbide, ER 201, the ratio of resin to fill was around twenty parts curing agent to as high as one one part by weight to seven parts by weight, and the hundred parts resin to around about fifty parts curing ratio of resin to curing agent, metaphenylene diamine, agent with the preferred ratio generally being one hundred Was 100 parts by weight to parts by weight. parts by weight of resin to thirty-five parts by weight of This product was tested and found to have a modulus curing agent, These curing agents are of the general 25 Of rupture of 9,300 p.s.i. at 70 F. and 4,800 p.s.i. at .formula 350 F. R1 R1 In any of the above examples either alpha alumina I (crystal form) or fused alumina (amorphous) can be R1N R NR1 used; however, it was proven that these substances pro- 'ded different modulus of rupture curves over a range identified hereinbefore. Among the useful curing agents v1 are, for example, diethylene triamine and metaphenylene of temperatures Thls 15 w? by 3 whlch 1ndcates that better strength qualities were demonstrated by dlamme and mlxtures thereof the al ha alumina at both ambi nt and lvat d t m- The following examples illustrate the various ratios of peratulgey h owever these substanjes can g choesen resms to cunng agents and the resultmg Propel-Hes 375 for their various qualities to provide optimum results EXAMPLE VII under varying conditions. Also, any of the above exam- A ceramic fin co osed of a1 1mm d ples can be made up of a cerannc fill which comprises throu h a mesh s i en was dr mixed fio o bt i n n frointo per-cent A1203 (a-himma) the reeven size distribuation of the graiins therein and then '40 manfnng parts g fi 8 g fz g s g as, orexampe: a, g, 1 orr -1 e il heated about approximately two latter two are commercially available as the minerals Ours; to remove any wajter t a Y Present 'rutile and zircon. The calcium oxide and magnesium oxide theremepoxy resm i lorohydnn f increase the thermal conductivity of the castable and the fliiuiii fifll$225335? oi-e aztmsrta it; ,5 ag at ensity ut are more expensive a itives. e mo uus 2332a:mgr;attenuates; of wa e are otte 1n w ie a e s owst e to erties Parts yh g d y g l l k curing agent, of the castables mixed with various fills in var yin perto one un re parts y weig t o t e a ove resin, was centagesn I v added to l mlxtul'e- 0 Relative to the above examples, it is to be understood a q g g 3 IZ EQ E ln l I $l 1 n y that the range set forth for vibration of the mixtures is a f Ore F 6 111 0 2? e Curlng Procmerely the optimum range in that while vibration may '2 't t ilsoi g fthetlnltltal t I -A' occur at a frequency lower than 2400-3600 vibrations per -saecurewasa .0 W00 0 this, t be casting was removed from the m l d an ti surfziz 5 3 3 1: gf e nigg lj z ii gggsegf egt gggfi gigfiy ig l gg bubble htlels1 and lclips were repaired. The B- 0f 0.10 inch. Likewise, should the frequency be increased ingwaso t e mo ed article at 250 F. for two hours and the amplitude may be decreased. 1 the C-stage curing was at 350.F. for two hours. It is also to be understood relative to the above exam After curing it was found the castable had a modulus ples that the heating of the dry ceramic fill may be of rupture at 70 F.7of 4,275 p.s.i. and at 350 F. offi accomplished by the mixing of the fill in its dry state 2,100p.s.1. r due to the friction heat generated by mixing.

.-. .5 j TABLEI [Fills in epichlorohydrin-Bisphenol A epoxy] Percent Clllll'l Modulus shrink- Density No. Fill rupture age (lbJitfi) 1 Until] (I 2 1 pbw res i iij pbw Al o grain 3 1 pbW resin, 6 pbw A1203 grain 4 1 pbw resin, 7 pbw A1203 grain 5 1 pbw resin, 8 pbw A grain"- 6... 1 pbW resin, 9 pbw A1203 grain... 7 1 pbw resin, 10 pbw A1203 grain s 1 pbW resin 8 pbW fill (90% A1,o 10% CaO) 9 1 pbW resin 8 pbW till (70% Mam -30% CaO) during curing and for high rtemperwture applications.

Items 1 through 7 of Table I indicate that optimum strength is obtained by using approximately 8 parts of A1 filler to one part of resin. It is believed that this may be because the adhesive bond of epoxy to filler is stronger than the cohesive strength of the epoxy itself. This being the case, as more filler is added, the filled resin depends more on adhesion than cohesion for its strength properties. When more than about 8 parts of filler are used with 1 part resin, the amount of filler becomes so excessive that effective cementing of the filler particles by the resin becomes more difiicult.

TABLE IL-GRAIN SIZE EFFECTS Percent curing Modulus Grain sizes fill shrinkage rupture Number 1 On 50 mesh 0. 25 7, 440 2 On 20 mesh 0. I9 4, 009 3 (20+50) mesh 0.30 2, 209 4 Mixed sizes:

(4+6 mesh) 4%. -6 8) 16 -8+20) 22%-. 20+28) 7 2 +35 The alumina grain size distribution for maximum strength is shown in Table II, along with the etfects of distribution change. Generally, the quantities of each of these mixed sizes may be varied between plus or minus 20 percent without appreciably affecting the compressive strength of the castable.

Table III makes a comparison between the plasticceramic and aluminum alloys.

TABLE III Plastic-ceramic composition for tools, etc.

(A) Basic Information (1) Composition: 1 part by weight plastic-8 parts by weight ceramic (2) Density:

(a) plastic-ceramic composition-170 l b./cu. ft.

or 0.1 lbt/cu. in.

(b) aluminum alloys-same (170 lb./cu. ft.) (3) Compressive strength (a) plastic-ceramic composition16,000 p.s.i;

(b) aluminum alloys (as cast) 12,00020,0( )0 (con- (a) plastic-ceramic composition8 10 in./in./ M 7 F. (b) aluminum--13 X 10* in./in./ F. (7) Cost (a) plastic-ceramic composition$.32/lb. (current cost) (b) aluminum-$1.13/lb. (aircraft grades) vstrength figures for the plastic-ceramic composition reflect measurements on unreinforce'd specimens. The strength hecomes considerably higher when Inhe composition is reinforced with steel rod. Such reinforcing is possible as the thermal expansion of the steel and the composition are compatible both Thus, contrary to the prior art, it has been discovered that an admixture of refractory oxide (including as a major constituent thereof aluminum oxide) and epoxy resin, when cured, have unexpected high tensile strength and is capable of extended use at elevated temperatures in excess of, for example, 250 F. The fact that the admixture of this invention can be cast into a variety of shaped articles prior to being cured and possess relatively low shrinkage when cured, enables the compositions to be used in a variety of articles including being formed or shaped into matrices or molds from which duplicate articles may be formed.

These matrices or molds were developed for use in fabricating heated forming tools for plastic-Fiberglas plastic-ceramic aggregates of this invention include heated and room temperature metal forming dies, models, surface plates, lavatories, sinks and fixtures and low cost corrosion and heat resistant hardware. Further applications have been in lay-up blocks, hydroblocks, stretch form blocks, draw dies, and with self-heat tools in which heating elements may be cast into the tools during fabrication.

Also, since the coefficient of thermal expansion of steel is approximately equal to that of the mixture, the use of deformed steel reinforcing rods inside heavy castings is sometimes desirable to increase the strength of the product, especially in resisting bending loads. The arrangement of how the rods are installed in the mold is illustrated in FIG. 5.

It will be understood by those skilled in the art that the embodiments of the invention here presented are by way of illustration only, and are meant to be in no way restrictive; therefore, numerous changes and modifications may be made, and the full use of equivalents resorted to, without departing from the spirit or scope of the invention as outlined in the appended claims.

What-is claimed is:

1. A high temperature plastic-ceramic castable, composition comprising an epoxy resin, 6 to 10 partsby weight ofa ceramic filler to each 1 part by weight of resin and 25 to'5O parts by 'weight of a curingagent for each 100 parts by weight of the resin in which: the epoxy resin is a resin selected from the group consisting of (a) diglycerl ethers, (b) novolac, and (c) polyolefins with peracetic acids; the ceramic filler is a member selected from the group consisting of (a) alumina, mixtures of (b) alumina with calcium oxide, (c) aluminawith magnesium oxide, ((1) alumina with titanium oxide, and (e) alumina with zircon said ceramic filler having mixed grain sizes as follows: v

' and, said curing agent is of the formula is.a member from the group consisting of H and a long chain saturated hydrocarbon of from 1 to 8 carbon atoms; and n is at least 1.

2. The composition of claim 1 wherein said filler is comprised of at least 70 percent by volume alumina, the ratio of resin to filler is l to 8, and the ratio of resin to curing agent is 100 to 25.

3. The composition of claim 1 wherein said ceramic filler is alumina having mixed grain sizes as follows:

Mesh: Percent -4+6 4 -6-1-8 16 8+20 22 -20+2s 7 28+35 35+4'8 4 48+65 7 65+lOO 11 100+150 -150+200 7 -200 2 10 filler is aluminum oxide employed in a ratio of 8 parts by weight to 1 part by weight of resin.

6. The composition of claim 1 wherein said epoxy resin is epichlorohydrin-bisphenol A and said ceramic filler comprises from about percent to percent by volume of alumina and the remaining volume selected from the group consisting of (a) calcium oxide, (b) magnesium oxide, (c) titanium oxide, and (d) zircon, a total of 8 parts by weight of said ceramic filler being used for 1 part by weight of resin.

References Cited UNITED STATES PATENTS 3,404,195 10/1968 Weinrich 26037Ep)X 3,170,890 2/1965 Boyd et a1. 26037('Ep) FOREIGN PATENTS 1,151,377 7/1963 Germany 26037(Ep) OTHER REFERENCES Harper; Electronic Packaging with Resins; McGraw- Hill Book Co., Inc.; 1961; pp. 41-44, 132-137, 140, and 141; Sci. Lib., TK 7870 H28.

MORRIS LIEBMAN, Primary Examiner L. T. JACOBS, Assistant Examiner 

